A,B = map(int, input().split())
H,W = map(int, input().split())

a = 0
b = 0
if H/B > W/A:
    a = (W/B*B)*(W/B*A)
else:a = (H/A*A)*(H/A*B)

if H/A > W/B:
    b = (W/A*A)*(W/A*B)
else:b = (H/B*B)*(H/B*A)
b = A*B

#print(a, b)
if a > b:
    print(int(a))
else:print(int(b))
print("")